Patent GB-756829-A (GB)
Title: Improvements in or relating to gas-pressure blasting devices
Inventor: JR EDWARD C FILSTRUP
IPC: F42B3/06
Filed: 1954-11-18
Abstract: 756,829. Blasting cartridges. ARMSTRONG COALBEAK CO. Nov. 18, 1954, No. 33421/54. Class 9(1) [Also in Group. XXVIII] A fluid-pressure blasting cartridge is provided with a steel body 10 connected to a venting head 84, the head 84 having lateral discharge ports 94 closed by a sleeve valve 136 and a forward end aperture in which a plunger 142 carrying the valve is slidably mounted. Gas under pressure is led into the body 10 through a tube 66 communicating with a metal tube 44 through connections housed in an end closure 14. An adapter 72 connecting the body 10 and the head 84 acts as an abutment for the rear end of a follower sleeve 156 and the head 84 is provided with grooves on each side of the ports 94 housing sealing rings 88, 98.. A vent 92 extends through the head 84 in the neighbourhood of a shoulder 90, which acts as a stop for the sleeve 156. In the forward end of the head 84 is an end closure 104 with diametrically opposed apertures 118 into which extends a shear rod 122 .seated against an annular washer 120 surrounding the forward end of the plunger 142. The shear rod is clamped by a plug 124 having an axial passage 126. Plug 124 has a cup-shaped end into which fits an annular member 130 locked to the plug by a snap-ring. A shoulder 144 on the plunger bears against the end wall of the sleeve valve, the valve being secured to the stem of the plunger by a nut 148 with a slight clearance between the parts so that the sleeve may tilt slightly relative to the stem. A spring 150 bearing against the shoulder 144 also bears against an annular plate 152 to hold resilient seals in the bore 108. After placing the device in a borehole, gas under pressure, e.g. from an air compressor, is connected to the tube 44. As the pressure increases there is a force tending to shear the rod 122, this force being the resultant of pressure on the plunger 142 and the effective pressure on the sleeve 156. On shearing of the rod 122, the valve sleeve 136 moves to the right of Fig. 1 clearing the ports 94 to vent the gas, the forward movement of the follower 156 being stopped by the shoulder 90. To reset the device, the plug 124 is loosened, broken parts of the rod 122 are removed, a new rod 122 inserted and the plug 124 is then tightened. To prevent overheating of the cartridge, the tube 66 terminates near the adapter 72 so that the expanding air leaving the tube has a cooling effect on the adapter and valve mechanism. To cool the gas-entry end of the device, ports 58 are provided in a fitting 54 connecting the tube 44 to the tube 66, Fig. 3. Housed in the closure 14 is a connector 40 having a frusto-conical head to receive the flared end of tube 44, a threaded member 48 with a flared mouth being mounted on tube 44 and screwed into the closure 14 to form a gas-tight seal. Aligned with the bore of the connector 40 is the fitting 54, the bore of which is enlarged to receive the tube 66. A retainer 68 on the tube 66 is pressed by a nut 60 into the fitting 54. To lessen the effect of impact on the device, an elastic or extensible conduit may be incorporated in the tube 66. This conduit may be of rubber reinforced with metal.